约1200年,treisoun,treson,“背叛;信任的背叛;不忠,信仰的违反”,来自盎格鲁法语treson,源自古法语traison“叛国,背叛”(11世纪;现代法语trahison),来自拉丁语traditionem(主格traditio)“交付,投降,传递,放弃”(西班牙语traicion的来源),名词形式来自过去分词词干tradere“交付,交出”,来自trans“过”(参见trans-)+ dare“给予”(来自原始印欧词根*do-“给予”)。是tradition的双生词。古法语形式受到动词trair“背叛”的影响。
Vpon Thursday it was treason to cry God saue king James king of England, and vppon Friday hye treason not to cry so. [Thomas Dekker, "The Wonderfull Yeare 1603"]
在古英语法中,high treason(约1400年)是指臣民违反对王冠或国家最高权力的效忠(其中high的意思是“严重的”);与petit treason区分,后者是指对臣民的叛国罪,例如仆人谋杀主人,伪造等。Constructive treason是一种司法虚构,即在没有叛国意图的情况下进行的行为,但被认定为具有叛国效果的行为,被惩罚为真正的叛国。这解释了美国宪法中对叛国罪定义的谨慎措辞。
Lord George Gordon was thrown into the Tower and was tried before Lord Mansfield on the charge of high treason for levying war upon the Crown. The charge ... rested upon the assertion that the agitation which he had created and led was the originating cause of the outrages that had taken place. As there was no evidence that Lord George Gordon had anticipated these outrages, as he had taken no part in them, and had even offered his services to the Government to assist in their suppression, the accusation was one which, if it had been maintained, would have had consequences very dangerous to public liberty. [W.E.H. Lecky, on the Gordon Riots (1780), in "History of England in the Eighteenth Century"]
中古英语中也有作为动词,treisounen(14世纪中期),“背叛,将敌人交给敌人之手”。